Optimal active immunotherapy of cancer should involve selectively potentiating the immune response to cancer specific antigens while reducing reactivity to self-antigens. Vaccine approaches are most likely to be effective in the setting of minimal cancer burden such as would occur after stem cell transplant (SCT). Therefore, the long-term goals of this project are to improve the effectiveness of SCT of hematopoietic neoplasms by safely increasing the immune response specifically directed at residual cancer cells using peptide vaccination. Much of the proposal focuses on WT1, a validated, commonly expressed tumor antigen. We also explore as a target the newly described mutated JAK2 kinase, responsible for many myeloproliferative disorders/These goals are reasonable because: 1) new understanding of the role of amino acid anchor motifs for MHC molecules in our target peptides and the strategic use of synthetic, heteroclitic, analog T cell epitopes. 2) the characterization of several peptide based vaccines for patients, including those to bcr/abl, WT-1, PR-1, and other oncogene associated targets as new cancer and leukemia associated tumor antigens. 3) the observation of clinical responses with the use of these peptide vaccines in patients with residual leukemia. Therefore, in this grant proposal we plan to extend our own work from the prior grant period and build on the published work of others into a better understanding of, and development of, specific immunotherapies directed to the oncogene products WT-1 and, for the first time, mutated JAK2 kinase. Previuosly, we focused on bcr/abl as a prototype target for vaccine therapy of CML and have progressed to multicenter trials. We build on this success here in new models directed at vaccine development against other important oncogene products. Aims 1 and 2 focus on WT1, a validated vaccine target found in many tumors and leukemias. Aim 1 is centered on discovery and characterization of novel WT-1 antigens. Aim 2A seeks to translate this knowledge in animals, in models of SCT and GVHD, and Aim 2B examines these antigens in humans. Aim 3 looks at the newly discovered, mutated JAK2 kinase, responsible for many myeloproliferative disorders, as a potential malignancy-specific target. There are important synergies between this project and project #4 of Richard O'Reilly in the development of the WT1 vaccine strategies. Relevance: Vaccines inducing or augmenting leukemia-selective T cell responses may reduce risk of relapse post transplant.